The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
An aspect of the invention relates to an apparatus for preparing food, comprising a food preparation chamber with an air-permeable bottom wall and an upper air discharge opening, a fan for moving hot air successively through the bottom wall, the food preparation chamber and the discharge opening, an air guide for returning the air from the discharge opening towards the bottom wall separate from the food preparation chamber, a heat radiator positioned in the upper part of the food preparation chamber and the air guide below the food preparation chamber and on top of a bottom part for directing the air flow essentially upwards into food present in the food preparation chamber
An apparatus of this type provides a method for the preparation of food wherein the food is heated from below by convection (by means of the air flow) and from above by radiation (by the heat radiator) simultaneously. The air, which is heated by the heat radiator, circulates within the apparatus and prepares the food (frying, cooking).
In an apparatus which heats food by means of convection a substantial amount of heat is lost because the air flow looses a substantial amount of its energy due to resistance in the flow path. Moreover, in many known apparatus the air circulates without having been in contact with the food.
Apparatus exist in which the air only can follow a path along the food, and in such apparatus the heat transfer towards the food is improved because the heat transfer is determined by the amount of heat present in the air flow and the magnitude of the surface the air flow can contact within a specified period of time.
In known apparatus much of this energy is lost due to resistance of the air flow within the apparatus. This negatively influences the air flow, speed of preparation and baking quality.
In known apparatus the air flow pattern basically is vertical or cyclonic. Due to its high upward speed a vertical air flow is very effective because the air only follows a short path before again reaching the heat source. However, such a vertical air flow requires a vast amount of energy for diverting the air which has started to circulate by means of the fan. This results in a substantial loss of air flow, time and baking quality and requires much power for the fan. Of course this will lead to an increased power consumption.
In a cyclonic air flow pattern the rotation of the air flow, in a known apparatus, will be determined by the shape of the food preparation chamber. The air follows the inner wall, resulting in air flowing along said inner wall with a high circumferential velocity, whereas in a central column the air substantially is static. The upward velocity of the air is minimal. This provides large differences in baking result between food present in a central area of the food preparation chamber and food present along the inner wall. Although a cyclonic air flow pattern requires much kinetic energy, it results in a worse and less consistant result.